Oil and gas recovery from tar sands



Nov. 24, 1959 G. J. w. SALOMONSSON 45 OIL AND GAS RECOVERY FROM TAR SANDS Filed May 25, 1953 5 Sheets -Sheet 1 FIG.\

1 g o o o o 3 o o o 3 l3 3 3 3 4 4 YAYAYAA AYAYAYAYA VAAYAYAY INVENTOR GOSTA J, w. SALO'MONSS'ON AT TORNEY Nov. 24, 1959 G. J.YW. SALOMONSSON 2,914,309

OIL, AND CAs RECOVERY FROM TAR SANDS Filed May 25, 1953 v 5 Sheets-Sheet 2 GASEOUS FUEL AIR AND/OR OXYGEN- PYROLYSIS VAPOURS a 9 OVERBURDEN NO TAR CONTENT VIRGIN TAR SAND ZONE WHERE PYROLYSIS TAKES PLACE ZONE WITH SAND COKE AIR AND/O OX I R 'YGEN PYROLYSIS, VAPOURS OVERBURDEN NO TAR CONTENT VIRGIN TAR SAND lo ZONE WHERE PYROLYSIS TAKES PLACE ZONE WITH SAND TAR i INVENTOR GOSTA J. w. SALOMONSSON ATTORNEY G. J. w. SALOMONSSON 2,914,309

OIL AND GAS RECOVERY FROM TAR SANDS Nov. 24, 1959 Fiied May 25, 1953 5 Sheets-Sheet 3A BURNING GASES AND F 6 PYROLYSIS VAPOURS GAS INLET TUBE I l GAS OUTLET TUBE OXYGEN-CONTAINING GAS MIXTURES OVERBURDEN NO TAR CONTENT ZONE WHERE PYROLYSIS HAS PARTLY OCCURRED ZONE WITH COKE PERFORATED TUBE VIRGIN TAR SAND ZONE WHERE PIROLYSIS occuRs F'RST CONNECTED v ZONE WITH COKE WHERE COMBUSTION occuRs E ZONE WITH OUTBURNED COKE T CONNECTED ELEMENT CONTENT OUTBUR- DEN PYROLYZED SAN D TIMEA 1 PERIODS TIME B7+0 I O INVEN'IB'R GOSTA J.W. SALOMONSSON THE ELEMENTS CONNECTED AT TIMES A AND 8 FIG. 9.

ATTORNEY Nov. 24, 1959' G. J. w. SALOMONSSON 9 OIL AND GAS RECOVERY FROM TAR SANDS 5 Sheets-Sheet 4 Filed May 25, 1953 GASEOUS FUEL AIR AND/QR OXYGEN GAS OUTLET F I G. 7

PYROLYSIS VAPOURS TAR SAND PYROLYSIS ZONE OVERBURDEN SAND COKE MOVABLE GAS FIRED ELEMENT INVENTOR GOSTA J. W. SALOMONSSON ATTORNEY Nov. 24, 1959 G. J. w. SALOMONSSON 5 3 011. AND GAS RECOVERY FROM TAR SANDS Filed May 25, 1953 5 Sheets-Sheet 5 FIG. 8

GAS

AIR AND/OR OXYGEN I GAS OUTLET TUBE MOVABLE GAS INLET TUBE OVERBURDEN ZONE WHERE PYROLYSIS HAS PARTLY OCCURRED PERFORATED TUBE 37 ZONE WITH COKE VIRGIN TAR SAND ZONE WHERE PYROLYSIS OCCURS ZONE WITH COKE WHERE COMBUST ION OCCURS ZONE WITH OUTBURNED COKE 4 INVENTOR GOSTA J. W. SALOMON'SSON ATTORNEY United States Patent OIL AND GAS RECOVERY FROM TAR SANDS Gosta Johan Wilhelm Salomonsson, Hallabrottet, Sweden, assignor, by direct and mesne assignments, of one-half to Svenska Skifferolje Aktiebolaget, Orebro, Sweden, :1 joint-stack company of Sweden, and one-half to Husky Oil Company, Cody, Wyo., a corporation of Delaware Application May 25, 1953, Serial No. 357,042

6 Claims. (Cl. 262-3) This invention relates to methods of recovering hydrocarbon containing products from tar sands in situ in the earth, to apparatus for enabling such methods to be carried out, and to the products resulting from such operations.

Various types of different mining and separating methods have been proposed in the prior art for the recovery of tar from tar sands. The yields obtained have been too small compared to the costs for mining, transporting, treating and disposal of tne sand. Among the methods which may be mentioned are separation by means of hot water, cold water, or solvents and further pyrolysis in retorts. The mining and handling of this cloggy material has offered a number of difiicult technical problems. In all of those methods the initial features involve mining and transportation of the mined material. After the separation, the heavy tar must be cracked to lighter compounds before it can be refined by the methods to produce products of use on the market.

Among the objects of the present invention are included methods of recovering hydrocarbon containing products from tar sands in situ, the separation being performed directly in the ground.

Other objects include the pyrolysis of the tar to produce lighter hydrocarbons, the volatile products of pyrolysis such as cracking being distilled off immediately and collected.

Further objects include apparatus enabling such operations to be readily carried out.

Still further objects include the hydrocarbons products produced by pyrolysis of the tar in the tar sand in situ.

Still further objects and advantages of the present invention will appear from the more detailed description set forth below, it being understood that such more detailed description is given by way of illustration and explanation only, and not by way of limitation, since vairous changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

In connection with that more detailed description, there is shown in the accompanying drawing, in

Figure 1, a plan view of one arrangement of heating elements for carrying out the present invention; in

Figure 2, a plan view of another arrangement; in

Figure 3, a plan view of a further arrangement; in

Figure 4, a vertical section through a field subjected to treatment in accordance with the present invention; and in Figures 5-9, vertical sections through fields illustrating additional methods of treatment in accordance with the present invention.

In accordance with the present invention, hydrocarbon containing products are produced from tar sands in situ in the earth by subjecting the tar sands in situ in the earth to heat to pyrolyze the tar in the sands and to form pyrolyzed hydrocarbons which are recovered.

Various types of tar sands deposits found in several parts of the world may be utilized. The most important 2,914,309 Patented Nov. 24, 1959 ice deposit is that of the Athabasca tar sands in northern Alberta, Canada. Such Athabasca tar sand is fairly typical of materials that can be utilized in accordance with the present invention and due to their availability will be employed to illustrate the present invention. The Y tar sand COIlSlStS of an intimate mixture of fine quartz sand constituting about by weight, a heavy and viscous black tar constituting generally from about 12- 17% by weight, with smaller quantities of water of about 2 to 5% by weight. The tar differs in many respects from petroleum and is an essentially different material. At room temperature it is semi-solid. The Athabasca deposits are approximately to 200 feet thick and are overlain by 0-200 feet overburden consisting of gravel, shale, limestone, etc.

It has been found that the physical and chemical properties of such tar sands require essential differentiations in the methods of treating such tar sands to recover hydrocarbon containing products therefrom in situ, that is without removal of the tar sand from the earth for treatment at some other locality.

In accordance with tne present invention instead of mining and handling the sand, the separation of hydrocarbon containing products from tne tar is performed directly in the earth. The method desirably employed includes pyrolysis, e.g. cracking of the tar to lighter hydrocarbons by heating the sand layers to such temperatures that the tar in tne tar sand is pyrolyzer or cracked. The volatile cracked products are distilled off immediately and collected as in drill holes through the layers, the drill holes being connected with a tube network.

In the pyrolysis of tar in the sand in situ, heat is supplied to pyrolyze the tar. Desirably the temperature for pyrolysis is from about 250 C. to about 380 C., but other ranges of temperatures can be employed depending on the effects sought. As the tar between the sand grains is heated above about 100 C., its water content (normally from about 2 to 5% by weight of the sand) is given off. At higher temperatures the tar becomes less viscous and begins to move downwardly between the grains by gravity. At about 250 C. thermal decomposition begins and as a result of the pyrolysis vapors of hydrocarbons (from methane up to heavy oil hydrocarbons) and related compounds are produced as well as oxygen, nitrogen and sulfur compounds. Phenols, ammonia and hydrogen sulfide are among products usually obtained. The vapors are recovered from the production bore-hole or gas-hole. In the movement of vapors toward the collection zone, where they come in contact with colder and more dense parts of the tar sand, the heavier components are condensed to the liquid state in which the tar is partly dissolved and diluted and flows more easily. After the pyrolysis, there is left be hind in the sand a coke like or carbon containing product which may be burned later.

The heat utilized for pyrolysis may be supplied to the heating zone in any desired way. Thus electrical elements inserted in tubes in drill holes may be employed as well as gas fired elements, superheated steam, etc., or heat may be obtained by combustion of the virgin tar sand or any cracked residues thereof left behind in the formation, the carbon in such cracked residues being readily available for this purpose. Where combustion of such residual carbon containing products is utilized to produce heat employed in other stages of the process, the combustion of such coke-carbon will generally not produce all of the heat necessary for pyrolysis of tar in the tar sand and in such cases may be sup.- plemented by utilization of combustible gases produced in the pyrolysis of the tar or from other sources. Since pyrolysis of the tar produces hydrocarbon vapors and combustible gases which latter have little utility other than for combustion purposes, the combustible gases may be separated from the volatile hydrocarbons present and the combustible gases utilized to supplement the source of heat as explained above.

The heating elements may be arranged in any desired Way in spaced heating zones desirably arranged in geometrical pattern which heating zones connect through passages in the earth with a gas or vapor recovery zone so that such gas recovery zone is surrounded by spaced heating zones. Such pattern may for example be that of a triangle, a square, or a hexagon, the triangular, square, or hexagonal pattern desirably covering the whole field, which is to be subjected to treatment. In the arrangement shown in Figure 1, heating elements 1, 1 are arranged hexagonally while gas outlets 2, 2 are positioned centrally of each geometrical figure of the pattern. In Figure 2, a square pattern is illustrated with heating elements 3, 3 and gas outlets 4, 4. A heating element may be placed in each triangle, square or hexagon and a gas recovery zone or gas hole positioned at the center of each of the triangles, squares or hexagons. A triangular pattern is shown in Figure 3 where a'combined heating ele ment 5 and gaseollecting tube 6 may be arranged in each corner of each triangle. The heating period length and distance between heating elements depends on the specific load on the element, that is the electrical power or fuel calories supplied per hour per unit length of the element. For example with electrical heating, specific loads of from 0.5 to 2.5 kw./meter may be utilized but these it should be understood are exemplary and may vary with particular conditions and operations being carried out. The most desirable load value to be employed may be determined by field tests under the particular conditions of operation in a particular field.

The condition which determines the heating period is that every part of the sand layer should be brought to the desired temperature necessary for complete pyrolysis of the tar. Desirably this temperature may be about 380- 400 C. (720750 F.). The heating period lengths of time will vary with the particular fields and operations being carried out but will generally lie within fairly reasonable limits as from 1 to 40 weeks.

The features referred to immediately above are particularly concerned with indirect heating methods as when heating elements are inserted in heating zones or drill holes. If the heat is produced in situ in the tar sand itself as by combustion of combustible gases or of coke-carbon in the formation produced from pyrolysis of the tar itself, or by combinations of such methods, the heat transfer may be improved in a number of ways. In such cases the maximum temperatures in the combustion zone may be higher and no tube strength restrictions are imposed. The combustion zone moves slowly and concentrically outward from the inlet points so that the heat transfer distance is thus diminished. The combustion gases flow toward the gas outlets thereby carrying heat from the hottest to the coldest portions of the tar sand. Consequently such methods of heat treatment improve the heating rates and cut the length of heating periods considerably. In utilization of a combustion element for heat treatment, a specific load corresponding for example to 1.0 kw./meter may be obtained for example by blowing an air quantity of about 15 cubic meters and a fuel quantity of about 1 cubic meter per minute per meter of element length. The air and fuel gas may be mixed at the burner head and ignited. In this way the combustion of the coke-carbon is initiated. As the coke is burned, the combustion zone spreads in all directions.

The combustion gases must overcome the flow resistance of the unburned coke and, at distances farther from the element, of the virgin tar-impregnated sand. As soon as the gases have penetrated through the barrier, the passage rapidly becomes wider due to the action of the hot gases. The tar is liquified and pressed away.

As well the sand as the coke after pyrolysis are permeable for oil vapours, combustion gases etc. The coke is, however, more permeable than the sand. This fact may be utilized for creating such passages in the oil-bearing strata that the oil vapors and gases preferably move towards the gas outlet point.

The sand is transformed to coke by means of heating the former. Thus there is formed a coke wall around the element hole. This coke formation starts during the hole drilling in the case where the drilling is performed by the drill burning method. If the element heating starts after the hole drilling, the thickness of the coke layer is larger, the longer is the heating time. Around the element tube there is thus created a passage for gas flow in vertical direction, upwards or downwards. At the same time as the coke is formed the pyrolysis takes place and oil .vapors and gases are liberated. In the zone where pyrolysis takes place a super-pressure is created, which forces the volatile products to flow in all directions, which are permeable.

The conducting of the heated tar and/or tar products may even be brought about by introduction of gas under pressure.

It the gas outlet is situated at the top of the sand layer the vertical gas passage should be open from the pyrolysis zone to the outlet point. This occurs if the pyrolysis zone, that is the heated part of the element moves downwards. If the outlet point is at the bottom of the sand layers, the pyrolysis zone should move from bottom upwards through the sand in order to create the necessary passage for the gases. This movement of the pyrolysis zone may be arranged by lowering or raising the burner equipment inside the element tube. If the heat is created by combustion of coke or gas directly in the layers, the burner which supplies air (and gas) for the combustion, may be moved upwards or downwards in the same manner and for the same purpose as described above. These matters are subsequently exemplified.

The hydrocarbon vapors and combustible gases etc., produced by pyrolysis of the tar in situ may be collected in any desired way. It is possible to collect vapors and gases in such a way that at least partial separation of the vapors from the gases takes place in the heating zone as can be accomplished by relative positioning of the points of entry of air or oxygen and fuel gases when used, and points of removal of the vapors and gases. The oil vapors are collected and subjected to further treatment such as condensation, distillation, refining, transport and byproduct recovery according to any desired methods at any point where such vapors may be conveniently treated.

The oil vapors and gases leave the zone, where they have been formed or liberated with a rather high temperature for example 350400 C. Part of their sensible heat content may be utilized for preheating combustion air or fuel or both by means of heat exchangers of any shape, either built together with the element tube and sunk in the element hole, or forming a separate equipment, connected to the top of the element tube, above the ground surface.

If heat is generated in the element or directly in the ground by combustion of any kind of fuel, also the sensible heat of the combustion gases may be utilized for the above-mentioned purpose.

The sensible heat content of the oil vapors and gases, formed through the pyrolysis may also be utilized for distilling the oil produced into such fractions of different boiling temperatures that may be found suitable for marketing or further refining purposes. This may be made in such manner that the hot gases, leaving the ground, are directly fed to a fractioning tower of conventional design. Thereby no, or only a part of the heat quantity which would otherwise have been used, must be supplied to the tower.

The products from the in situ pyrolysis of tar sand are of better quality and are more easily refined than products from other methods of oil recovery. If tar is extracted f om sand, after mining, with hot or cold water gasoline, are due to such characteristics of the in situ.

method as the long duration of the heat treatment and the relatively low temperature during the pyrolysis. As an example of the properties of an oil, which can be obtained by the in situ method, may be mentioned the following analysis of an oil, obtained in a direct test:

Spec. gravity, 20 C 0.87 Refractive index 1.490 Viscosity, 20 C centistokes 7.0 Viscosity, 50 C do 2.2 Sulphur content percent by weight..- 2.8 Bromine number 35 The virgin tar contains about 4% by weight of sulphur in the form of sulphur-compounds. Through the lengthy heating of the rock by using the in situ method these sulphur compounds are cracked, whereby at least part of the sulphur is obtained in the incondensable gases in the form of hydrogen sulphide. The hydrogen sulphide can be separated from the gas and transformed to elemental sulphur by means of known processes (for instance the AlkaZid-Claus method).

In methods for pyrolysis of tar sands in situ it is necessary to have drill holes or bore holes in which heating elements may be placed. The production of drill holes or bore holes in tar sand frequently offers difficulties. It has therefore been found desirable to utilize methods for hole drilling in tar sand as disclosed in the application of G. Salomonsson Serial No. 298,189 filed July 10, 1952, now patent No. 2,833,516, in which the hole drilling is performed by means of a stream of air or oxygen, desirably heated, directed toward the sand. The hot air or oxygen initiates a combustion of the tar between the sand grains which are thus liberated. The sand grains may be transported pneumatically to the surface for example by means of the ascending current of combustion gases. If the tar content is not high enough to maintain the combustion, an additional amount of fuel for instance gas may be supplied to the burner. The tar in the surrounding portions of the sand is partially cracked by the heat liberated at the drilling operation. Such cracking results in a coke residue which hardens the hole walls. This hardening may be so strong that no casing of the wall is necessary.

Since the drilling burner and the heating element for producing pyrolysis of the tar in situ in the tar sand may have analogous functions such as sunnlving air and gas under pressure to the sand layers, the drilling and pyrolysis heating may be carried out in a single operation.

As an example of the processes mentioned above, the following data is given.

The oil recovery process may for example be performed by drilling holes with a diameter of 3 inches in a triangular pattern, covering the whole field with a shortest hole distance of 2.5 meters. The drilling through the overburden may be performed in the conventional way. When the overburden is thin, some part of the upper tar sand layer may also be drilled in this way. For drilling through the tar sand, drilling burners according to the patent No. 2,833,516 may be used. Some part of the layers under the tar sand is also drilled through. When drilling with the drilling burner through the tar sand there is formed 6 a columnar coke layer around the hole so that no casing of the hole is necessary as pointed out above.

Figures 4 and 5 exemplify a gas fired element in position in the whole tar sand layer. After the hole is drilled, the drilling burner is removed and a combined heating element and gas outlet tube is sunk into the hole. As shown in Figure 4, the gas outlet tube 7 is sunk just to the upper part 8 of the tar sand when the overburden 9 is thick. When the overburden is thin, or if there is no overburden at all, the gas outlet tube 7 is desirably sunk down through some part of the tar sand as shown in Figure 5, where this upper part of the tar sand will compensate for the thin overburden as a covering cap. Elsewhere the pyrolysis vapours will come up everywhere between the holes. The heating element 10 is situated between the bottom of the gas outlet tube 7 and the bottom layers with no tar content. This latter is especially important because it is thus possible to heat some part of the bottom layer and in such a way avoid the tar flowing to the bottom layer and remaining there. Gaseous fuel and oxygen containing gas mixtures are supplied through fuel inlet 11 and air inlet 12 respectively to the element 10 of such character and in such quantities that a quantity of heat of about 700 kcal. is liberated per hour and per meter of the element length.

The column shaped heat zone proceeds concentrically out from the element tube so there will be a zone 13 with sand coke nearest the hole followed by the zone 14 where the pyrolysis takes place. The progress of the heating process is followed by temperature measurement in the coldest part of the field, that is in the center of the triangle between three heating elements. When the temperature at this point has increased to 400 C. which normally happens about about 5 months heating, the heating is stopped since every part of the sand has been brought to pyrolysis temperature.

The pyrolysis vapours and gases are collected through the gas outlet 7, which is situated at the top of the tar sand layer. The super pressure, created in the sand during the pyrolysis, is suflicient to maintain the gas flow in the rock and through the gas-collecting tubes. The super pressure in the rock may be regulated to a desired value by means of valves (not shown), inserted in every gas tube.

Depending on local conditions, such as availability and price of gaseous fuel, quality of uncondensable gases obtainable from the specific kind of tar sand being heated, etc., it may be perferable to use the calories of the sand coke for heating, e.g. in the following way:

The triangular pattern as set forth in Figure 3 also shows a hexagonal pattern by combining 6 triangles with a common corner. This arrangement may also be used in combustion of the sand coke. Firstly, a part of the tar sand is pyrolyzed around each combined heating element and gas-collecting tube to such an extent that the temperature between two such holes is high enough, say about l00l50 C'., that the viscosity of the tar here is low enough to permit gases passing from one hole to another adjacent hole. By throttling the gas outlet holes, it is possible to develop a higher super pressure in the tar sand layer and thus hasten the production of passages between the centre hole and one of the surrounding holes. Thereafter the heating elements are removed and in the centre hole of a hexagon, a perforated tube is sunk. As shown in Figure 6, an oxygen containing gas mixture is distributed to the whole sand layer 15 through the perforations 16 of the tube 17. The ignition can be started either by preheating the oxygen containing gas mixture to a sufiicient temperature or by dropping a self igniting substance or mixture of substances into the element hole 18. Depending on the greater or lesser permeability and the greater or lower carbon content of the sand coke, the combustion proceeds more or less rapidly and thus gives shape to a more or less regular combustion 7 zone 19, the temperature of which will be 800-1000 C. From this zone 19, the heat is conducted to cooler parts of the layers. In the zone 20 where the temperature is about 250-400" C., the pyrolysis takes place. The pyrolysis vapours and combustion gases pass together to the six adjacent holes situated at the angles of the hexagon, these holes now serving only as gas outlet holes 21. As shown in Figure 6, the combustion gases and pyrolysis vapours passing to a gas outlet hole 21, pass firstly virgin tar sand 22 and then the tar sand 23 which partly has been pyrolyzed and ultimately the zone 24 round the gas outlet hole which consists of a tar sand coke column. The methods of collecting the gases and main taining the super pressure in the tar sand are the same as in the above mentioned gas fired element process.

The supply of oxygen containing gas mixtures is interrupted when the sand temperature is 400 C. in the zone 23 where the tar sand first has partly pyrolyzed round the gas outlet holes 21.

The inlet tubes 18 can also be arranged in a triangular pattern with each tube at the angles of the triangle. The combustion gases and pyrolysis vapours are then collected in a special hole which may be situated in the center of each triangle between the elements.

The supply of oxygen containing gas mixtures is even in this case interrupted when the sand temperature in the triangle center is about 400 C. If the supply of oxygen in the gas mixtures is regulated to about 0.15-0.20 cubic meter per hour and per meter of element length, and if the distance between the element holes is about 2.5

meters, the process will take about months before the mentioned temperature is reached.

In the above mentioned examples the heat has been substantially equally distributed along the whole length of the hole in the tar sand layer. It has also been mentioned that the tar will flow downwards to the bottom layers. At least partly opposing such action, some part of the bottom layer also has been warmed up by the heating elements. To further prevent such action it may be desirable to start the heating of the sand from the bottom and then raise the heating elements upwardly through the hole. In this way the tar, when it flows downwards, meets the heat from the bottom, pyrolyzes and the pyrolysis vapours go upwards through the gas outlet tube. An example of the arrangement is shown in Figure 7. The movable gas fired element 25 is here situated at the bottom of the hole 26. The gaseous fuel and oxygen containing gas mixture enter through two concentric tubes 27 and 28 respectively down to the gas fired element 25. The combustion gases from the element 25 pass through another concentric tube 29 to a chimney, e.g. via a heater exchange, not shown in the figure. The three concentric tubes may consist of connectable parts, e.g. meter long tubes. The element with these tubes are hung up on a wire 30 which runs over a pulley arrangement 31. The pulley 32 is set up in a tower 33 whose height is somewhat more than the concentric tube parts, in this example thus about ll meters. The element equipment hangs freely in the gas outlet pipe 33 for pyrolysis vapours and the coke hole, 26.

At the burning of the sand coke as before mentioned, it is also possible to distribute the combustion gases and thus the heat unequally. Figure 8 shows how the oxygen containing gas mixture and possibly also a gaseous fuel pass through two concentric tubes 34 and 35 respectively to the bottom part of the hole 36 in which a perforated tube 37 is inserted. The outer movable concentric tube 35 is of such diameter that it can just be moved up and down through the tube 37 through the overburden 38 and the tar sand 39. The part of tube 37 which passes through the tar sand should be perforated. The lifting gear arrangement and other features may be the same as that described in Figure 7. The combustion gases 8 pass through the sand to the outlet gas tube 40 in the same way as described in Figure 6.

Figure 9 illustrates how the pyrolysis of the sand may be carried out by a number of elements to obtain unequal distribution of the heat. Here is shown, eight rows 41 of holes and how the heating front from them appears. The distance between the bottom 42 and the top 43 of the tar sand layers 44 is here divided in seven parts and the height of the heating elements is about the same as the height of the said seventh. When an element has been connected for a suitable period it is moved upwards a seventh of that distance between the top and the top of the sand layer. The raising of the burners (elements) to the next higher level may take place contemporarily in all connected rows of wells at the same time as a new well row is connected, adjacent to the most lately connected of the previously connected rows. When the new row is connected the burners in this row of wells are at their lowest level. Thus the different rows of burners will form a stepwise arrangement. The first connected element has at the time A been moved six times and connected for seven periods and the whole zone around this tube is pyrolyzed at this time. The next element has at the same time (A) only been connected for six periods and thus first a period later (at time B)'the whole sand layer around this tube has been pyrolyzed. In the same manner the following elements are connected more later and for the eighth element there is no connection until at time B. Thus there is attained a zig-Zag formed pyrolysis front which is moving along the field.

In a similar manner also the movable inlet tubes for oxygen containing gas mixtures may be arranged.

Having thus set forth my invention, I claim:

1. In a method of recovering hydrocarbons containing products from tar sands in situ in the earth, the step consising essentially of subjecting said tar sand in situ in a vertical drill hole to heat progressively vertically and columnarly along the walls of the borehole at a temperature of from about 250 C. to about 400 C. to pyrolyze the tar by cracking to produce volatile lighter hydrocarbons and coke thereby to form a tube wall of hard sand coke surrounding the columnar heating zone, said coke being of greater permeability than the tar sand.

2. The method as set forth in claim 1 in which the heat is supplied to the tar sand from a heating zone progressively moving from a lower to an upper zone.

3. The method as set forth in claim 1 in which the heat is supplied to the tar sand from a heating zone pro gressively moving from an upper to a lower zone.

4. A three-stage method of recovering hydrocarbon containing products from tar sands in situ in the earth by subjecting said tar sand in situ in the earth to heat and thereby pyrolyzing the tar in said sand to form pyrolyzed hydrocarbons and recovering volatile hydrocarbon products from the pyrolyzed tar products, characterized by the steps of initially heating the virgin tar sand deposit'progressively from its upper level to its base to a temperature of between 250 C. and 400 C. progressively to form substantially vertical cylindrical heating zones which extend from the upper level of the deposit to its base and within which the tar is pyrolyzed to form a substantially cylindrical vertical wall of hard sand coke around each cylindrical heating zone, subsequently continuing the heating at pyrolysis temperature so as to cause the wall of each individual heating zone to expand columnarly until it reaches a sand coke wall of a cylindrical heating zone and finally causing the vapors and gases produced by hydrolysis to flow through the sand coke, due to its higher permeability for gas than virgin tar sand, to some of said cylindrical heating zones, in which heating has been terminated to convert such zones into outlet holes.

5. The method as set forth in claim 4 in which the sand coke wall is produced by means of movable heating elements which in accordance with the heating conditions desired can be inserted within and removed out of the tar sand deposit.

6. The method as claimed in claim 4 in which the cylindrical heating zones are distributed over the surface of the ground covering the tar sand deposit so as to constitute the angles of at least a three sided regular polygonal pattern, the holes of Which zones upon formation of the coke wall by removal of the heating elements are transformed into discharge holes while a new cylindrical heating zone is formed by supplying oxygen containing gas mixtures through a tubular heating element inserted into the tar sand deposit in the center of the polygon.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,188,737 Hixon Jan. 30, 1940 2,280,851 Ranney Apr. 28, 1942 2,365,591 Ranney Dec. 19, 1944 2,584,605 Merriam et al. Feb. 5, 1952 5 2,630,307 Martin Mar. 3, 1953 2,634,961 Ljungstrom -d Apr. 14, 1953 2,688,464 Payne Sept. 7, 1954 2,694,550 Aitchison et al Nov. 16, 1954 2,734,579 Elkins Feb. 14, 1956 10 2,780,449 Fisher et al. Feb. 5, 1957 2,833,516 Salomonsson May 6, 1958 FOREIGN PATENTS 464,909 Canada May 9, 1950 15 (Corresponding U.S. 2,497,868Feb. 21, 1950) 121,737 Sweden May 25, 1948 123,138 Sweden Nov. 9, 1948 

1. IN A METHOD OF RECOVERING HYDROCARBON CONTAINING PRODUCTS FROM TAR SANDS IN SITU IN THE EARTH, THE STEP CONSISING ESSENTIALLY OF SUBJECTING SAID TAR SAND IN SITU IN A VERTICAL DRILL HOLE TO HEAT PROGRESSIVELY VERTICALLY AND COLUMNARLY ALONG THE WALLS OF THE BOREHOLE AT A TEMPERATURE OF FROM ABOUT 250*C. TO ABOUT 400*C. TO PYROLYZE THE TAR BY CRACKING TO PRODUCE VOLATILE LIGHTER HYDROCARBONS AND COKE THEREBY TO FORM A TUBE WALL OF HARD SAND 